Thallium (Tl) is an extremely harmful metal that is substantially distributed in the environment. It can threaten human health via consumption of food potentially derived from Tl-contaminated agricultural production. Little information is available on how to utilize biochar to remediate Tl contamination in agricultural soils. More efforts are urgently needed to be devoted to developing effective techniques to empower biochar with high selectivity of Tl in agricultural soils. In this review, we provided comprehensive information on Tl contamination in agricultural soils. We also discussed recent developments and assessed the current status of biochar applications. We briefly reviewed the bridge between biochar preparation technology and utilization wherein further developments can exhibit potential in terms of Tl remediation. Hence, biochar is expected to exhibit excellent Tl remediation performance in contaminated agricultural soils with promising application prospects. The obtained knowledge provides further insights into the remediation of Tl contamination in agricultural soils.
Vegetable gardens are increasingly common in urban areas and can provide numerous societal benefits; however, contamination with potential toxic elements (PTEs) due to urbanization and industrialization is cause for concern. The present study aimed to assess the source of contamination and pollution levels in urban garden soils, as well as the health risks for adults and children consuming vegetables grown in such environments. Various types of vegetable samples and their corresponding soils from 26 community gardens were collected throughout Chengdu City in southwestern China. The results showed that leafy vegetables, particularly lettuce leaves and Chinese cabbage, had relatively higher levels of Cd (0.04 mg/kg FW) and Pb (0.05 mg/kg FW), while higher levels of As (0.07 mg/kg FW), Cr (0.07 mg/kg FW), and Hg (0.003 mg/kg FW) were found in amaranths, tomatoes, and Houttuynia cordatas, respectively. The pollution indices revealed that the vegetable purplish soils were relatively more polluted by Cd and As, and the concentrations of these metals in vegetables were correlated with their concentrations in the soils. Principal component analysis grouped the PTEs in two dimensions that cumulatively explained 62.3% of their variation, and hierarchical clustering identified two distinct clusters indicating that Cr originated from a unique source. The health risk assessment revealed that exposure to As and Cd induced the greatest non-carcinogenic risk, whereas Cr was most likely to cause cancer risks. Furthermore, contaminated vegetable consumption was riskier for children than adults. The critical factors contributing to PTE contamination in vegetable gardens were determined to be vegetable species, total soil element content, soil pH, and soil organic matter content. Overall, Cr and As pollution present the greatest concern, and community health care services must enact more effective regulatory and preventative measures for urban gardens in terms of PTEs.
Adoption of crop residue amendments has been increasingly recommended as an effective management practice for mitigating greenhouse gas emissions while enhancing soil fertility, thereby increasing crop production. However, the effect of biochar and straw on nitrous oxide (N2O) and methane (CH4) emissions in soils of differing pH remains poorly understood. Three treatments (control (i.e., no amendment), maize straw, and biochar derived from maize straw) were therefore established separately in soils with different pH levels, classified as follows: acidic, neutral, and alkaline. N2O and CH4 were investigated using a static chamber–gas chromatography system during 57 days of a mesocosm study. The results showed that cumulative N2O emissions were significantly higher in acidic soils than in other experimental soils, with the values ranging from 7.48 to 11.3 kg N ha−1, while CH4 fluxes ranged from 0.060 to 0.089 kg C ha−1, with inconclusive results. However, a weak negative correlation was observed between log N2O and log NO3-N in acidic soil with either biochar or straw, while the same parameters with CH4 showed a moderate negative correlation, suggesting a likelihood that these amendments could mitigate GHGs as a result of the NO3-N increase in acidic soils. It is also possible, given the alkaline nature of the biochar, that incorporation had a significant buffer effect on soil acidity, effectively increasing soil pH by >0.5 pH units. Our findings suggest that for the rates of application for biochar and straw used in this study, the magnitude of reductions in the emissions of N2O and CH4 are dependent in part on initial soil pH.
Phyllosphere-associated microorganisms affect host plant’s nutrients availability, its growth and ecological functions. Tobacco leaves provide a wide-area habitat for microbial life. Previous studies have mainly focused on phyllosphere microbiota at one time point of tobacco growth process, but more is unknown about dynamic changes in phyllospheric microbial composition from earlier to the late stage of plant development. In the current study, we had determined the bacterial and fungal communities succession of tobacco growth stages (i.e., seedling, squaring, and maturing) by using both 16S rRNA sequencing for bacterial and ITS sequencing for fungi. Our results demonstrated that among tobacco growth stages, the phyllospheric bacterial communities went through more distinct succession than the fungal communities did. Proteobacteria and Actinobacteria exerted the most influence in tobacco development from seedling to squaring stages. At maturing stage, Proteobacteria and Actinobacteria dominance was gradually replaced by Firmicutes and Bacteroidetes. Network analysis revealed that Proteobacteria, as the core phyllospheric microbia, played essential role in stabilizing the whole bacterial network during tobacco development, and consequently rendered it to more profound ecological functions. During tobacco development, the contents of leaf sugar, nicotine, nitrogen and potassium were significantly correlated with either bacterial or fungal communities, and these abiotic factors accounted for 39.3 and 51.5% of the total variation, respectively. We overall evinced that the development of tobacco phyllosphere is accompanied by variant dynamics of phyllospheric microbial community.
Green manure (GM) is widely adopted for agricultural productivity and sustainability. The present study supplemented the GM effect with that of water retaining agent (WRA) to enhance the sustainability of tobacco planting purple soils in Sichuan Province, China. The study employed three GM legumes varieties (Trifolium repens, Vicia villosa and Medicago sativa), while the WRA used was polyacrylamide at different application rates (0, 30, 90, 150 and 210 kg/ha). The results revealed that the average concentration of trace elements ranged from 0.86 to 1.18 mg/kg, 22.2 to 26.5 g/kg, 78 to 426 mg/kg, 16 to19 mg/kg, and 69 to 76 mg/kg for Mo, Fe, Mn, Cu, and Zn, respectively. Compared to actual soil concentration, Mn was increased by adding 150 or 210 kg/ha to M. sativa fertilized soil. Zn was increased by combining any WRA rate with V. villosa or 150 kg/ha WRA with T. repens. The combination of 90 kg/ha WRA with M. sativa, and 30 kg/ha WRA with either T. repens or V. villosa decreased Fe. Then, all the treatments reduced soil Mo and Cu. Therefore, these GM and WRA affected the soil environmental conditions associated with different responses of individual soil trace elements.
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